Field
Embodiments of the disclosure relate generally to iron alloys having low or no chromium content.
Description of the Related Art
Abrasive and erosive wear is a major concern for operators in applications that involve sand, rock, or other hard media wearing away against a surface. Applications which see severe wear typically utilize materials of high hardness to resist material failure due to the severe wear. These materials typically contain carbides and/or borides as hard precipitates which resist abrasion and increase the bulk hardness of the material. These materials are often applied as a coating, known as hardfacing, through various welding processes or cast directly into a part.
The most commonly used wear resistant ferrous materials for casting and hardfacing contain chromium as an alloying addition. Chromium as an alloying element typically serves two purposes, improving hardenability and forming chromium containing carbides, borides, and/or borocarbides. Both these purposes improve the wear performance of the material. However, when an alloy containing chromium is cast or welded, carcinogenic hexavalent chromium fumes are released. The amount of chromium released is a largely function of the chromium content of the alloy with increasing chromium levels resulting in greater release. Hexavalent chromium levels released from these alloys commonly exceed standards, proposed standards, and guidelines set by OSHA, NIOSH, CARB, and other regulatory bodies. In areas that manufacture chromium bearing alloys, chromium levels frequently exceed EPA specified maximums. Recently, even lower acceptable safe levels have been proposed and new materials are needed that facilitate compliance with current and future laws and regulations.
U.S. Pat. Nos. 8,474,541 and 6,702,905, each of which is hereby incorporated by reference in its entirety, teach a chromium bearing Fe-based alloy which forms transition metal borides.
There have been some specific attempts at developing chromium free and wear resistant ferrous alloys. For example, U.S. Pub. No. 2013/0294962 (“Wallin”), hereby incorporated by reference in its entirety, describes a chromium free hardfacing consumable. The wear resistance of the alloys described in the application comes from a combination of niobium or titanium carbides and borides or borocarbides of which the metallic constituent comprises mostly iron.
Similarly, U.S. Pat. Nos. 7,569,286, 8,268,453, 4,673,550, 4,419,130, each of which is hereby incorporated by reference in its entirety, teach alloys, including chromium free alloys that rely on borides substantially for their wear resistance. These borides comprise predominantly Fe and Ti based borides.
U.S. Pat. No. 4,235,630 (“Babu”) hereby incorporated by reference in its entirety, teaches a wear resistant alloy comprising a mixture of ferroboron and molybdenum. Babu teaches a volume and mole fraction of borides that exceeds the criteria described in this disclosure. Further Babu describes alloys where the matrix comprises substantial amounts of eutectic Fe—Mo intermetallics or iron borides.